(1) Field of the Invention
The present invention relates generally to optical hydrophones, and more particularly to an optical hydrophone in which light transmission through a material incorporating air-filled voids or bubbles is affected by the acoustic induced resonance of the air-filled voids or bubbles, the affected light beam serving as a means for measuring the acoustic waves causing such resonance.
(2) Description of the Prior Art
Towed acoustic receiver arrays are used in military and civilian applications to detect acoustic signals in the water. Traditional towed acoustic receiver arrays take the form of linear arrays of hydrophones mounted inside a flexible hose, the array being connected to a towing vessel by a tow cable. Although the data from these hydrophones may be transmitted through the tow cable optically, the measurement of the sound pressure levels is done electro-mechanically. More recently, innovative arrays developed for U.S. Navy applications use optical fibers wound around mandrels to detect sound. However, arrays made from either electromechanical hydrophones or mandrel-wound optical fiber hydrophones are fairly large in diameter. This leads to the use of larger, heavier and more expensive handling equipment (e.g., winches, motors and storage reels) for the storage, deployment and retrieval of the towed acoustic receiver array.
Accordingly, it is an object of the present invention to provide a linear hydrophone array that is small in diameter.
Another object of the present invention is to provide a hydrophone for use in a towed acoustic receiver array.
Still another object of the present invention is to provide a linear hydrophone array that is small in diameter.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, an optical hydrophone includes a housing defining a chamber. The housing is acoustically transparent to acoustic waves at a frequency of interest. An optically transparent material fills the chamber and has air-filled voids (e.g., bubbles in the material, air-filled microspheres, etc.) defined therein that expand and collapse thus resonating within the material when the acoustic waves impinge on the material. Light is introduced into the material (e.g., a light source such as a light transmitting optical fiber) and passed therethrough. The light passed through the material is received/detected where the light passed through the material is affected by the air-filled voids resonating within the material. In terms of an optical hydrophone array, the light passed through the material is transferred into another optical fiber and then along the array of hydrophones. The array must be calibrated prior to use in order to measure the amount of light attenuation for a given acoustic signal level.